1. Field of the Invention
This invention relates to a new mold release composition for the production of molded products with self-releasing properties based on polyurethanes or polyureas, a mixture of compounds with isocyanate reactive groups containing this composition, a process for the production of elastomeric molded products having a closed surface layer using these mixtures and the molded products obtained by this process.
2. Description of the Prior Art
The production of elastic molded products based on polyurethanes or polyureas by the reaction of mixtures of a polyisocyanate component, relatively high molecular weight compounds containing isocyanate reactive groups, low molecular weight chain lengthening agents and auxiliary agents and additives inside closed molds is known, for example from DE-AS No. 2,622,951 or EP-B No. 0,081,701. In these prior art processes, the reaction mixtures are generally prepared in accordance with the reaction injection molding (RIM) method and introduced into their mold immediately after they have been prepared. The resulting molded products are generally removed after a very short time in the mold. For carrying out this process in practice, especially for a large scale production of such molded parts, the ease with which the product can be released from its mold is of major importance. This is determined to a large extent not only by the use of "external mold release agents," i.e. mold release compositions used to coat the mold before it is filled, but also by the use of so-called "internal mold release agents." These "internal mold release agents" are incorporated in the reaction mixture, with the result that the molded product obtained adheres less firmly to the surface of the mold than it would if it contained no mold release agent. For the production of elastomeric molded products, in particular with a density in the range of 0.8 to 1.4 g/cm.sup.3, combinations of zinc salts of long chained carboxylic acids, in particular zinc stearate, and certain organic compounds containing tertiary amine nitrogen atoms have proved to be very suitable. An example of a typical compound of this kind containing tertiary amine nitrogen atoms is the addition product of about 5 mol of propylene oxide to 1 mol of ethylene diamine. These compounds containing tertiary amine nitrogen atoms act as solvents for the zinc salt which is generally only sparingly soluble and at the same time they impart a certain solubility to the zinc stearate in the mixtures of compounds containing isocyanate reactive groups with which the polyisocyanates are to undergo reaction. Mold release compositions of this kind and their use for the production of elastic molded products have been described, for example, in U.S. Pat. Nos. 4,519,965, 4,581,386 and 4,585,803.
One disadvantage of these prior art mold release compositions, however, is that they have only a limited capacity to impart solubility, with the result that when they are added to mixtures of compounds containing isocyanate reactive groups of the kind used in the process described above, the mixtures must be worked up immediately after addition of mold release composition since the mold releasing effect diminishes rapidly when the mixtures are left to stand. In practice, therefore, the mold release compositions are generally added to the compounds containing isocyanate reactive groups only shortly before manufacture of the molded products. The same, incidentally, also applies to mold release compositions consisting of zinc salts, in particular zinc stearate, and compounds containing primary amino groups, for example the compositions recommended in EP-A No. 0,119,471.
It was an object of the present invention to provide new mold release compositions which would not have the disadvantage of rapidly losing their mold release effect when stored in the mixtures used to prepare the molding.
This problem has now been solved by means of the mold release compositions according to the invention which are described below. These mold release compositions according to the invention contain certain selected tertiary amines of the kind described below as solvents or compatibility imparting agents for the zinc salt, in particular zinc stearate. The mold release compositions according to the invention are distinguished in particular by a combination of the following advantages:
1. The mold release effect obtained with the new mold release compositions is at least equal to that obtainable with prior art mold release compositions. PA0 2. Mixtures of compounds containing isocyanate reactive groups of the kind used for the production of elastomeric molded products and containing the mold release compositions according to the invention need not be worked up immediately after their preparation (i.e., addition of the mold release composition to the other components) since molded products with excellent self-releasing properties can be obtained from the completely prepared mixtures even if these mixtures have been kept in storage. In practice this means that the manufacture of molded products need no longer prepare fresh mixtures at frequent intervals by mixing the mold release composition with the other compounds. PA0 (A) about 10 to 75% by weight, based on a total weight of components (A) and (B) of at least one zinc salt of a straight chain or branched, saturated or unsaturated aliphatic carboxylic acid having 8 to 24 carbon atoms PA0 (B) at least one organic compound which is liquid at room temperature and corresponds to the formula EQU H.sub.2 N--(--CH.sub.2).sub.m --X PA0 X denotes an organic group containing nitrogen and/or oxygen, selected from the following: ##STR1## wherein R.sup.1 and R.sup.2 denote identical or different alkyl groups having 1 to 10 carbon atoms or together with the nitrogen atom and optionally oxygen or a C.sub.1 -C.sub.5 -alkyl substituted nitrogen atom as an additional hetero atom form a heterocyclic ring containing 6 ring atoms, PA0 R.sup.3 and R.sup.4 denote identical or different alkyl groups with 2 to 10 carbon atoms or together with the nitrogen atom and optionally an oxygen atom or a C.sub.1 -C.sub.5 -alkyl substituted nitrogen atom as an additional hetero atom form a heterocyclic ring containing 6 ring atoms, PA0 R.sup.5 denotes a straight chain or branched alkyl group with 2 to 10 carbon atoms or a group of the formula ##STR2## wherein R.sup.6 represents a straight chain or branched alkylene group with 2 to 8 carbon atoms and R.sup.1 and R.sup.2 have the meanings already indicated, PA0 R.sup.7 denotes an alkyl group with 3 to 10 carbon atoms, PA0 m represents an integer with a value from 2 to 10, PA0 n represents an integer with a value from 2 to 5 and PA0 o represents an integer with a value from 2 to 8. PA0 (a) at least one organic compound in the molecular weight range of 400 to 12,000 having at least two isocyanate reactive groups, PA0 (b) about 5 to 50% by weight, based on the weight of component (a), of at least one organic compound in the molecular weight range of 62 to 399 which contains isocyanate reactive hydrogen atoms and is difunctional in isocyanate addition reactions and PA0 (c) at least one mold release agent PA0 I: a polyisocyanate component containing at least one di- or polyisocyanate in which all of the isocyanate groups are aromatically bound PA0 II: a reactant containing an internal mold release agent and compounds containing isocyanate reactive groups PA0 (b.sup.1) Polyhydroxyl compounds in the above mentioned molecular weight range such as ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,3-dihydroxypropane, 1,4-dihydroxybutane, 1,6-dihydroxyhexane, trimethylolpropane or glycerol; PA0 (b.sup.2) Diamines containing aromatically bound primary amino groups such as 1,4-diaminobenzene, 2,4-diaminotoluene, 2,4'- and/or 4,4'-diaminodiphenylmethane or, preferably, aromatic diamines of the kind containing an alkyl substituent in at least one ortho-position to each amino group, in particular those containing at least one alkyl substituent in the ortho-position to the first amino group and two alkyl substituents, each with 1 to 4 carbon atoms, in the ortho-position to the second amino group. Particularly preferred are those diamines of the kind which contain an ethyl, n-propyl and/or isopropyl substituent in at least one ortho-position to the amino groups and optionally methyl substituents in other ortho-positions to the amino groups. The following are examples of such preferred or particularly preferred diamines: 2,4-diamino-mesitylene, 1,3,5-triethyl-2,4-diaminobenzene, 1,3,5-triisopropyl-2,4-diaminobenzene, 1-methyl-3,5-diethyl-2,4-diaminobenzene, 1-methyl-3,5-diethyl-2,6-diaminobenzene, 4,6-dimethyl-2-ethyl-1,3-diaminobenzene, 3,5,3',5'-tetraisopropyl-4,4'-diaminodiphenylmethane and any mixtures of such diamines. 1-methyl-3,5-diethyl-2,4-diaminobenzene and commercial mixtures thereof with up to about 35% by weight of 1-methyl-3,5-diethyl-2,6-diaminobenzene, based on the mixture, are particularly preferred. PA0 (d.sup.1) State of the art mold release agents of the kind described, for example, in DE-OS No. 1,953,637, DE-OS No. 2,121,670, DE-OS No. 2,431,968, DE-OS No. 2,404,310, DE-OS No. 2,319,648, DE-OS No. 2,356,692, DE-OS No. 2,363,452, DE-OS No. 2,427,273 or DE-OS No. 2,431,968, which may optionally be used in addition to the mold release component (c) according to the invention. It is also possible to also use the mold release agents described in U.S. Pat. No. 4,519,965 or U.S. Pat. No. 4,581,386 together with the mold release component (c) according to the invention. This means above all that component (c) may also contain the compatibilizers described in these patents in addition to components (A) and (B). Thus it may, for example, be appropriate to also add to the mixture of components (A) and (B) amine-initiated polyetherpolyols such as the addition product of 5 moles of propylene oxide to 1 mol of ethylene diamine and/or polyether polyamines having primary amino groups such as polypropylenoxides having terminal primary amino groups and molecular weights of from 200 to 600 which components may be present in component (c) in an amount of up to 80% by weight, preferably up to 50% by weight and more preferably up to 30% by weight based on the total weight of component (c). PA0 (d.sup.2) Catalysts for the isocyanate polyaddition reaction, in particular tertiary amines or organic tin compounds of which examples are given in EP-B No. 0,081,701. These catalysts, used in quantities of about 0.01 to 10% by weight, preferably about 0.05 to 2% by weight, based on the weight of component (a), are added particularly if component (a) consists predominantly or exclusively of polyether polyols of the type exemplified above. If components (a) and (b) consist exclusively of compounds containing amino groups, catalysts may also be added but are generally superfluous.